1. Field of the Invention
The invention relates generally to a self-adjusting assembly and method for close-tolerance spacing, and it more particularly relates to a SQUID probe microscope assembly and method for measurements of room-temperature samples for close tolerance squid-to-sample spacing.
2. Related Art
The information contained in this section relates to the background of the art of the present invention without any admission as to whether or not it legally constitutes prior art.
Microscope assemblies employing a scanning super-conducting quantum interference device (SQUID) probe have been employed in the past for measurements of room-temperature samples. For example, reference may be made to an article entitled xe2x80x9cCLOSED-CYCLE REFRIGERATOR-COOLED SCANNING SQUID MICROSCOPE FOR ROOM-TEMPERATURE SAMPLESxe2x80x9d by E. F. Fleet, et al, published in American Institute of Physics (Aug., 2001), which is incorporated herein by reference. This was achieved by employing the SQUID in an evacuated dewar having a window position therein. In this regard, the sample under test was positioned in close proximity on the room-temperature side of the window, and the SQUID probe tip was positioned inside the dewar in close proximity to the cold side of the window so that the probe tip would be disposed in a close tolerance spacing relative to the sample under test.
However, when the SQUID probe was deactivated, for example, such as when not in use, the SQUID probe expands axially as a result of thermal expansion due to the warming of the SQUID. Due to the close spacing with the window, the expanding probe tip could contact and break through the thin membrane window. Such a situation would be highly undesirable and destructive, because the window is expensive to replace, and the loss of vacuum within the dewar could cause extensive damage to the expensive SQUID.
In an attempt to overcome this problem, others have provided a mechanism for moving the window to the SQUID tip during operation of the SQUID microscope as explained in the aforementioned article. Thus, after the measurement is taken, the window is moved away from the probe tip.
In this manner, during the deactivation and warming of the SQUID probe assembly, the thermally expanding probe tip would not tend to engage the window, thereby causing damage to the unit.
However, the window must be moved into its adjusted position relative to the probe tip each time a measurement is to be taken. Such an operation is necessarily time-consuming, and does not always result in precisely the same spacing each time the adjustment is made. Thus, the measurements may not always be consistent. The adjustment of backing the window away from the probe tip must be accomplished at the end of each use of the SQUID probe assembly and at the end of each day of operation. Thereafter, it must be readjusted, in some instances, in three axes.
Due to differential temperature shrink rates in various components, conventional SQUID/pickup coil arrangements are placed in close proximity to room-temperature samples by adjusting the xe2x80x9ctailxe2x80x9d or tip of the dewar with, for example, a bellows or sliding mechanism of the xe2x80x9cwindow,xe2x80x9d as explained in the foregoing article. Alternatively, the SQUID probe itself could be re-positioned. Thus, the serious nature of the problem due to the cryogenic temperature induced shrinkage in the cold super-conductive components relative to the vacuum housing, which must remain at room temperature during operation when room temperature samples are to be measured.